Google Desktop is still on the server
In 2015, I visited the Google Desktop site on the Wayback Machine and tried to download it. I found that it was stored on dl.google.com and tried it outside of the archive.
As it turns out, Google never removed the final release from their download server, although there are no official links to it as it was discontinued about eight years ago.
Only the core gadgets included with the software can be placed in the Google Sidebar at this time, and even then not all of them may work.